Processes for the production of amines by the catalytic reductive coupling of a primary or secondary amine with a nitrile are known and widely used to produce the corresponding secondary and tertiary amines. The resultant amines find utility as additives for fuels, catalytic promoters, surfactants, biocides and in numerous other applications.
An object of many of these processes is the development of a more selective process for reductive amination of nitrites to produce tertiary amines, especially fatty (.gtoreq.C8) nitrites, by reaction of the corresponding nitrile with a secondary amine. The preferred reaction is described in Equation 1. ##EQU1##
However, selectivity often suffers, owing to a competing reaction pathway: a) reduction of the nitrile to the corresponding primary amine, and b) subsequent coupling of that amine with a second equivalent of nitrile to generate a secondary di(alkyl)amine. The pathway to this high molecular weight byproduct is described by Equation 2. ##EQU2##
A problem associated with byproduct di(alkyl)amine (ADMA), particularly byproduct di(fatty alkyl)amine, is that not only is it difficult to separate from the desired (fatty alkyl)dimethylamine but the separation is inefficient and energy intensive owing to the high boiling points of the ADMAs.
Representative patents which describe the reductive coupling of nitrites with amines are as follows:
U.S. Pat. No. 5,648,545 discloses the catalytic amination of a wide variety of nitrites by reacting a nitrogen compound such as ammonia, or a primary or secondary amine with the nitrile at temperatures of from about 80 to 250.degree. C. and a hydrogen pressure of 1 to 400 bar. The catalytic amination is carried out in the presence of hydrogen and the catalyst is comprised of a reduced copper oxide/zirconium oxide. Alkali metal carbonate is added to the catalyst prior to reaction. An exemplary nitrile included N-methylaminopropionitrile and representative amines reacted therewith included mono and dimethylamine.
Canadian Patent 834,244 discloses a process for continuously producing higher molecular weight secondary and tertiary amines by reacting higher molecular aliphatic nitrites with volatile primary or secondary amines. The fatty acid nitrites have a carbon content from 8 to 22 carbon atoms and include lauryl and stearyl nitrile and the low boiling amines include dimethylamine, diethylamine, etc. The catalyst is an alkali-modified copper-chromium catalyst with the alkylation being conducted at a temperature of 120 to 180.degree. C. and 180 to 210 atmospheres hydrogen pressure. Salts of alkali metals used in preparing the alkali-modified catalysts included those of potassium and sodium.
U.S. Pat. No. 5,869,653 discloses a process for the hydrogenation of nitrites to produce primary amines. In the catalytic hydrogenation of aliphatic nitriles, the nitrile is contacted with hydrogen in the presence of a sponge or Raney.RTM. cobalt catalyst employing lithium hydroxide as a promoter. A wide variety of aliphatic nitriles (C.sub.2-30) are suggested as being suited for conversion to the primary amine by reaction with hydrogen.
U.S. Pat. No. 5,847,220 discloses a process for the catalytic hydrogenation of a cyanopropionaldehyde alkyl acetal in the presence of a nickel or cobalt catalyst promoted with alkali metal hydroxide to form aminobutyraldehyde alkyl acetals, i.e., the primary amine derivative of the cyanoalkyl acetals. The background in the patent discloses a variety of processes for the hydrogenation of nitriles, but these processes generally deal with the hydrogenation of the nitrile itself, rather than a reductive alkylation by the reaction of the nitrile with a primary or secondary amine.
U.S. Pat. No. 5,557,011 discloses a process for producing diamines by reductive coupling of secondary amine with an aliphatic nitrie. In the background of the art, palladium/carbon catalysts were used as the primary reductive coupling catalyst. The improvement in the process wherein palladium was used as a catalyst resided in utilizing an oxidic support, such as a gamma alumina, silica, titania, zirconia, etc. which may be modified by inclusion of up to 15 wt % metal oxides of subgroups IB-VIIB, or Group VIII of the periodic table. Preparation of di-tert-amines from the corresponding dinitriles and secondary amines with palladium supported on an oxide (specifically, on an oxide selected from the group consisting of .gamma.-alumina, silica, titania, or zirconia) or on that oxide treated with an alkali metal/alkaline earth oxide was shown.
U.S. Pat. No. 5,894,074 discloses a process for the preparation of tertiary amines from nitriles and secondary amines utilizing a palladium catalyst. The improvement in the process utilizing palladium as a catalyst or catalysts incorporating small amounts of calcium oxide, alumina magnesium oxide, etc., resided in the inclusion of a small amount at least one further metal selected from the group of 1B and Group VIII, as well as cerium and lanthanum on a support. Examples of the latter class of catalysts include 0.5 wt % palladium/alumina with 20% calcium oxide and 1.0 wt % palladium/alumina with 20% magnesium oxide.